Patients

Adult patients with American Society of Anesthesiologists physical status I–II, aged 20–70 years, who were scheduled to undergo elective surgery under general anesthesia were enrolled in this study. We excluded patients who were likely to encounter difficulties or pain when actively performing the jaw and neck exercises: Patients with cognitive disorders, temporomandibular joint disorders, or cervical spine diseases. For safety reasons, we excluded patients under consideration for awake intubation using a fiber-optic bronchoscope, such as those with craniofacial anomaly or mechanical airway obstruction. Patients with tracheostomy or who were to receive oropharyngeal surgery during this protocol were also excluded. Enrolled patients were randomly allocated to either the exercise or the control group, using a computer-generated randomization code (Random Allocation Software Version 1.0; University of Medical Sciences, Isfahan, Iran). The allocation ratio was 1:1. Randomization was performed by an independent anesthesiologist in each hospital. These individuals were only involved in patient allocation and coaching of the exercise, and not in any aspects of anesthesia, data analysis or interpretation.